A generally cool dude who had ideas about just about everything behavioral. He also had a great sense of humor. One of the first Americans to make a big splash into the field.
Often called the 'father of experimental psychology,' Wundt felt that psychology should be conduced more like other sciences and set up the first psychology laboratory.
Developed ecological psychology. The basic idea: we can learn all we need to know about the world directly from patterns of light (or sound).
No student can make it through intro psychology withough running in to the infamous Milgram studies on obedience.
Also a behaviorist, but this time using operant conditioning (changing behavior patterns through the use of rewards and punishment).
A behaviorist through and through, his work in classical conditioning was very influential.
I can't imagine a famous psychologists page without him. Though many disagree with his theories, his ideas still pervade popular culture.
Possibly the most influential developmental psycholgist in history.